Electromagnetic conveyor system

ABSTRACT

A conveyor system for conveying electrically conductive articles such as aluminum cans. The conveyor system comprises a plurality of coils below the top surface of an electromagnetic conveyor at a junction between an infeed conveyor and a discharge conveyor. The coils propagate electromagnetic flux waves that induce currents in the electrically conductive articles that force the articles to follow a conveying path from the infeed to the discharge conveyor. Dead spots on the electromagnetic conveyor can be eliminated by adjusting the coil drive waveforms.

BACKGROUND

The invention relates generally to power-driven conveyors and moreparticularly to conveyors conveying electrically conductive articles,such as cans, electromagnetically. Conveyors are used to transportarticles through manufacturing processes. The transport of emptyaluminum beverage cans can be difficult in transitions where the cansare transferred from one conveyor to another. The lightweight cans areprone to tipping at the transitions and to stranding on transfer deadplates. Manual intervention is required to deal with toppled andstranded cans. But manual intervention increases manufacturing costs andrisks contamination of the cans. And if not dealt with, the stranding ofcans can result in the costly mixing of can batches.

SUMMARY

One version of a conveyor system embodying features of the inventioncomprises a first conveyor conveying electrically conductive articles ina first direction to an exit end, a second conveyor conveying theelectrically conductive articles from an entrance end in a seconddirection different from the first direction, and a diverter forming ajunction between the exit end of the first conveyor and the entrance endof the second conveyor The diverter includes an entrance adjacent to theexit end of the first conveyor receiving the electrically conductivearticles on a top surface from the exit end of the first conveyor and anexit adjacent to the entrance end of the second conveyor. Coils arearranged in a matrix of contiguous first and second zones below the topsurface. The coils in each of the first zones produce an electromagneticflux wave that forces the electrically conductive articles on the topsurface above the zone to move in the first direction. The coils in eachof the second zones produce an electromagnetic flux wave that forces theelectrically conductive articles on the top surface above the zone tomove in the second direction. At least some of the zones along theentrance are first zones and at least some of the zones along the exitare second zones. The electrically conductive articles are directed fromthe entrance to the exit by the coils in the first and second zones andonto the second conveyor.

Another version of a conveyor system embodying features of the inventioncomprises a first conveyor conveying electrically conductive articles ina first direction to an exit end and a second conveyor conveying theelectrically conductive articles from an entrance end in a seconddirection. The angle θ between the first direction and the seconddirection is given by 0°<θ≤90°. A diverter forms a junction between theexit end of the first conveyor and the entrance end of the secondconveyor. The diverter includes an entrance adjacent to the exit end ofthe first conveyor receiving the electrically conductive articles on atop surface from the exit end of the first conveyor and an exit adjacentto the entrance end of the second conveyor. Coils arranged in parallelbelow the top surface produce an electromagnetic flux wave that forcesthe electrically conductive articles on the top surface above the coilsto move in a third direction. The angle α between the first directionand the third direction is given by 0°<α<θ. The electrically conductivearticles are directed from the entrance to the exit by the coils andonto the second conveyor.

Yet another version of a conveyor system embodying features of theinvention comprises a first conveyor conveying electrically conductivearticles in a first direction to an exit end, a second conveyorconveying the electrically conductive articles from an entrance end in asecond direction different from the first direction, and a diverterforming a junction between the exit end of the first conveyor and theentrance end of the second conveyor. The diverter includes an entranceadjacent to the exit end of the first conveyor receiving theelectrically conductive articles on a top surface from the exit end ofthe first conveyor and an exit adjacent to the entrance end of thesecond conveyor. Coils are arranged in an arc below the top surface fromthe entrance to the exit. In a plan view perpendicular to the topsurface, each of the coils has a narrow end at the inside of the arc andan opposite wider end at the outside of the arc. The electricallyconductive articles are directed from the entrance to the exit by thecoils and onto the second conveyor.

Another version of a conveyor system embodying features of the inventioncomprises an electromagnetic conveyor that includes an entrance overwhich electrically conductive articles are transferred onto a topsurface and an exit over which electrically conductive articles aretransferred off the top surface. Coils are arranged below the topsurface in an array and produce electromagnetic flux waves causingforces that move the electrically conductive articles across the topsurface from the entrance to the exit. A controller drives the coilswith drive waveforms characterized by periodic pulses that periodicallyincrease the forces acting on the electrically conductive articles inlow-force regions on the top surface to enhance movement of theelectrically conductive articles.

Still another version of a conveyor system embodying features of theinvention comprises an electromagnetic conveyor that includes a topsurface, an entrance over which electrically conductive articles aretransferred onto the top surface, an exit over which electricallyconductive articles are transferred off the top surface, and a pluralityof coils arranged below the top surface in individual zones. The coilsproduce electromagnetic flux waves causing forces that move theelectrically conductive articles through the zones across the topsurface from the entrance to the exit. Controllers associated with thezones drive the coils with drive waveforms having different frequenciesor phase angles in adjacent zones to enhance movement of theelectrically conductive articles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a portion of a conveyor system embodyingfeatures of the invention for conveying electrically conductivearticles, such as cans.

FIG. 2 is an isometric view of the conveyor system of FIG. 1 with thecans removed.

FIG. 3 is a top plan view of coil modules in a diverter as in theconveyor system of FIGS. 1 and 2.

FIGS. 4A and 4B include elevation and top plan views of adjacent coilmodules in two different electromagnetic conveyors usable in a conveyorsystem as in FIG. 1.

FIG. 5 is a top plan view of an electromagnetic diverter with staggeredcoils in coil modules usable as an alternative diverter in the conveyorsystem of FIG. 1.

FIG. 6 is a top plan view of another version of a diverter havingobliquely arranged coils alternatively usable in a conveyor system as inFIG. 1.

FIG. 7 is a top plan view of an alternative diverter with an arcuatearrangement of coils usable in a conveyor system as in FIG. 1.

FIG. 8 is a side elevation view of a coil as in FIG. 7 with a uniformcore thickness and a varying winding thickness. FIGS. 8A and 8B arecross sections of the coil of FIG. 8 viewed along sight lines 8A and 8B.

FIG. 9 is a side elevation view of a coil as in FIG. 7 with a taperedcore thickness.

FIG. 10 is a side elevation view of a coil as in FIG. 7 with a uniformcore and winding thickness.

FIG. 11 includes top plan and side elevation views of a portion of anarcuate diverter as in FIG. 7, but with inner and outer coil sets.

FIG. 12 is a side elevation view of a coil winding usable in a conveyorsystem as in FIG. 1 with a winding crossover region along a short side.

FIG. 13 is a side elevation view of a coil winding usable in a conveyorsystem as in FIG. 1 with a winding crossover region along a long side.

FIG. 14 is a block diagram of a drive system for a conveyor system as inFIG. 1.

FIG. 15 shows one phase of a coil-drive waveform produced by the drivesystem of FIG. 14 using pulsed operation to eliminate dead spots.

FIG. 16 shows a portion of the waveform of FIG. 15 enlarged.

FIG. 17 shows corresponding phases of the coil-drive waveforms producedby the drive system of FIG. 14 for two adjacent coil zones to eliminatedead spots.

DETAILED DESCRIPTION

A conveyor system embodying features of the invention is shown in FIGS.1 and 2. The conveyor system 20 has an infeed conveyor 22 and anoutfeed, or discharge, conveyor 24—both shown as belt conveyors in thisexample. The infeed conveyor 22 conveys electrically conductivearticles, such as aluminum cans 26, in a first conveying direction 28 toan electromagnetic conveyor 30. In this example the electromagneticconveyor is configured as a diverting conveyor, or diverter, having anentrance 32 adjacent to an exit end 34 of the infeed conveyor. Thedischarge conveyor 24 receives the cans 26 at an entrance end 35 over anexit 33 of the diverter 30. In this example, the diverter 30 isrectangular—more precisely, square—with the entrance 32 and the exit 33on adjacent sides. The discharge conveyor 24 conveys the cans 26 in asecond conveying direction 29 different from the first conveyingdirection 28. The diverter 30 diverts the cans 26 on its top surface 36from the first conveying direction 28 to the second conveying direction29. In this example the diverter 30 serves as a 90° corner unit forminga junction between the exit end 34 of the infeed conveyor 22 and theentrance end 35 of the discharge conveyor 24. Although the infeed andoutfeed conveyors 22, 24 are shown as belt conveyors in this example,they could be any kind of conveyor that is suitable for conveying theparticular electrically conductive articles being handled. And theelectromagnetic conveyor 30 can instead be configured as an in-lineconveyor in which the cans are not turned, but pass straight through toa discharge conveyor in line with the infeed conveyor.

As FIG. 2 shows, the diverter 30 has a plurality of coils 38 arrangedbelow the top surface 36 in a matrix of contiguous zones: first zones 40and second zones 41. The coils 38 in the first zones 40 produceelectromagnetic flux waves that force the cans in the first zones tomove in the first conveying direction 28 as indicated by the arrowsdepicted in the zones. The coils 38 in the second zones 41 produceelectromagnetic flux waves that force the cans in the second zones tomove in the second conveying direction 29. The electromagnetic fluxwaves produced by the coils 38 in both zones 40, 41 propagate in thecorresponding first or second conveying direction 28, 29 and inducecurrents in the electrically conductive cans 26. The induced currentsproduce induced secondary fields that interact with the primary fieldsof the flux waves to create the force acting on the cans to move them inthe corresponding direction. Thus, the coils 38 in each zone serve asthe stator of a linear induction motor (LIM) in which each of theelectrically conductive cans 26 is analogous to a LIM rotor.

Although the first and second zones 40, 41 in the diverter 30 can be ofdifferent lengths as in FIG. 2, each zone can be constructed of one ormore identical coil modules 42, 42′, as shown in FIG. 3. Coils in eachcoil module 42, 42′ are housed in an enclosure or are embedded in apotted structure. The upper surfaces of the enclosures or structures canform the top surface 36 of the diverter 30 if they fit close togetherwith narrow seams between adjacent coil modules 42, 42′ to avoid tippingthe cans 26. The top surface 36 of the diverter 30 can alternatively beformed by a sheet or other structure providing a flat conveying surfacecovering the coil modules 42, 42′. First coil modules 42 form the firstzones 40, and second coil modules 42′ form the second zones 41.

In this example the matrix of contiguous first and second zones 40, 41is a square matrix of the identical coil modules 42, 42′ arranged infour rows R1-R4 and four columns C1-C4. The rows R1-R4 are aligned inthe second conveying direction 29 and perpendicular to the firstconveying direction 28, and the columns C1-C4 are aligned in the firstconveying direction and perpendicular to the second conveying direction.Furthermore, in this example, there are eleven second coil modules 42′forcing cans in the second direction 29 toward the exit 33 of thediverter 30 and five coil modules 42 forcing cans in the first direction28 away from the entrance 32. The coil module 42′ in the row R1 closestto the entrance 32 and the column C4 closest to the exit 33 is in asecond zone 41. And all the coil modules 42′ in the column C4 closest tothe exit 33 are in second zones 41. Three of the four coil modules inthe row R1 closest to the entrance 32 of the diverter 30 are in firstzones 40.

In this particular arrangement of coil modules 42, 42′ and zones 40, 41,the number of coil modules in contiguous first zones 40 decreasesmonotonically row by row away from the entrance 32. (The row R1 closestto the entrance 32 has three coil modules 42 in first zones 40; the nextrow R2 has two; and the third and fourth rows R3, R4 have none.) Cansfed onto the left side of the diverter 30 at the entrance 32 are pushedin the first zones 40 in the leftmost columns C1, C2 toward the secondzones 41 in the far rows R3, R4. Cans immediately to the right of thoseare pushed in the first zone 40 on the entrance row R1 and the thirdcolumn C3 to the second zone 41 in the second row R2. Cans fed onto thediverter 30 along its right side 45 and received in the second zone 41are pushed immediately toward the exit 33. In this way cans closer tothe right side 45 of the diverter 30 make a sharper turn to the rightthan those cans closer to the left side to help maintain the width ofthe mass of cans.

Of course, other arrangements of the zones and coil modules arepossible. For example, the coil module in the first row R1 and thefourth column C4 could be in a first zone to help induce cans onto thediverter 30 before their direction is changed. As another example, thematrix of zones could be arranged as a non-square rectangular array ofcoil modules. Or each zone could be made of a single coil module whoselength defines the length of the zone. And the number of zones and coilmodules could be greater or less than shown in FIGS. 1-3. An in-lineelectromagnetic conveyor is constructed with all the coil modules in asingle zone or in multiple zones all directing cans in the samedirection from the entrance to an opposite exit without a change indirection.

FIGS. 4A and 4B show two different side-by-side coil arrangements aspart of a diverter or as all or part of an in-line conveyor. FIG. 4Ashows two side-by-side coil modules 42A, 42B in adjacent zones Z1, Z2.Each coil 46 is wound around a core 48: for example, a laminated ironcore such as a silicon-iron (SiFe) core. In this example each coilmodule 42A, 42B has six coils 46. Opposite ends of the cores 48 have astepped structure of alternating protrusions 50 and recesses 52 thatmate with the protrusions and recesses of the core of an adjacent coilmodule to form a longer zone. The coils 46 on each core 48 are spacedapart across gaps 54. The ends of the coils 46 of side-by-side coilmodules 42A, 42B are offset along the coils' magnetic axes 55 to fit inthe gaps 54. The resulting overlap of the coil ends helps eliminate deadspots in low-force regions in the diverter. FIG. 4B shows twoside-by-side coil modules 42A′, 42B′ in adjacent zones Z1, Z2. The coils46 in each zone Z1, Z2 are wound around a single core and are closelyspaced so that little of the core is uncovered by the windings. Thecoils 46 in the adjacent zones Z1, Z2 are individually side by side withno axial offset and do not overlap the ends of the coils in the abuttinglaterally adjacent zone.

FIG. 5 shows an alternative diverter 60 arrangement of staggered firstand second zones 56, 57. Cans in the first zones 56 are moved in thefirst conveying direction 28 by the coils 46, and cans in the secondzone 57 are moved in the second conveying direction 29. An oblique lineof demarcation 62 separates the first zones 56 from the second zones 57.Each module 58 is parallelogram-shaped. The coils 46 in each module 58are offset lengthwise from each other to form the stagger along linesparallel to the demarcation line 62 and oblique to the first and secondconveying directions 28, 29. The staggered zones 56, 57 reduce low-fluxareas in the diverter 60 compared to the rectangular zones in thediverter 30 of FIGS. 1-4. Another version of an electromagnetic diverterfor electrically conductive articles is shown in FIG. 6. In this versionall the coils 64 in the diverter 66 are arranged geometrically withtheir magnetic axes 65 parallel and oblique to the first and secondconveying directions 28, 29. The flux wave produced by the oblique coils64 travels in a third direction 68 oblique to the first and seconddirections 28, 29. The angle θ between the first and second directions28, 29 is given by 0°<θ≤90°. In this example, θ=90°. The angle α betweenthe first and third directions 28, 68 is given by 0°<α<θ. Cans fed ontothe diverter 66 are immediately pushed diagonally toward the dischargeconveyor 24 in the third direction 68.

Yet another version of an electromagnetic diverter is shown in FIG. 7.The diverter 70 defines a curved track. In this example the curved trackis an arc subtending a 90° angle. Each of the coils 72 has a narrow end74 at an inside of the arc and a wider end 75 at the outside of the arc.The coils 72 are driven by a three-phase coil drive according to theA-B-C phasing arrangement φ1. One alternative is driving the coils withan apparent six-phase coil drive sequence φ2, which can be achieved witha three-phase coil driver by alternating the winding polarities asindicated by the φ2 phase sequence.

FIGS. 8-10 show cross sections of alternative coils usable in thecurved-track diverter 70 of FIG. 7. The coil 84 in FIG. 8 has alaminated core 86 of uniform thickness, i.e., constant height, along itslength. As shown in the cross sections of the coil 84 in FIGS. 8A and8B, the inside end 74 is laterally narrower than the wider outside end75 and the narrow inside end 74 is taller than the wider outside end 75.The coil windings at the narrow inside end require more layers than atthe wider outside end to keep a constant number of turns of a uniformlythick wire.

In FIG. 9 the stack of iron-core laminations 76 is tapered in thickness(height). The thickness T increases from the inside end 74 of the coil78 to the outside end 75. Because the coil 78 is generally trapezoidalin a plan view—wider at the outside end 75 than at the inside end 74—thewindings at the outside are distributed over a greater distancelaterally, and so the depth of the winding layers is less to form thecoil with a constant outer thickness (height) along its length.

Another alternative coil 80 is shown in FIG. 10. Like the coil 78 ofFIG. 9, the coil 80 has a constant thickness (height) along its length.And the thickness T of the coil's laminated core 82 is also uniformalong its length so that the ratio of the thickness of the coil to thethickness of the iron core is constant along the length of the coil 80.Because the outside end 75 of the coil 80 is wider, the coil windingsare distributed laterally over a greater width and are not as deep asthe winding layers at the narrower inside end 74.

FIG. 11 shows a portion of a curved diverter as an alternative to thatof FIG. 7. The diverter 90 is constructed of two concentric arcs 92, 93of coils 94, 95. (Only three coils are shown in each arc to simplify thedrawing.) The inner arc 92 lies inside the outer arc 93.

As shown in FIGS. 12 and 13, the coils 96, 96′ for all the examples canbe orthocyclically wound to minimize the volume occupied by thewindings. In the rectangular coil configuration shown, the orthocycliccrossover region of the coils is confined to one side of the coil. InFIG. 12 the crossover region 98—i.e., the region where the windingscross over each other to achieve the tight packing of orthocyclicwindings—is formed on one of the short sides. In FIG. 13 the crossoverregion 99 is formed on one of the long sides, such as the bottom sideaway from the top surface of the diverter to minimize the gap betweenthe iron core and the conveyed articles and to minimize dead spots inthe low-force boundary regions along the short sides of laterallyadjacent coils where the net field strength required to move cans islow. The coils 96, 96′ in FIGS. 12 and 13 have magnetic axes 97 directedalong the length of the coils' cores and parallel to the top surface ofthe diverter.

A controller for driving the coils in all the examples is shown in FIG.14. The controller 100 is a multiphase controller shown in this exampleas a three-phase controller operating as three current sources drivingthe coils 102A-C in each phase A, B, C through coil drivers 104A-C andseries capacitors 105A-C. Each zone in the diverters of FIGS. 1-6 or inan in-line electromagnetic conveyor could have a dedicated controller.All the first zones of diverters could be driven electrically inparallel by a first single controller, and all the second zones could bedriven by a second single controller. In-line conveyors and thediverters in FIGS. 6 and 7 could be driven by a single dedicatedmultiphase controller. And each arc in the diverter in FIG. 11 could bedriven by its own multiphase controller.

A programmable processor 106 connected to the controller 100, can beconnected to other such controllers to coordinate control of all thecoil zones. Or the processor 106 could be integrated into eachcontroller 100 instead. A vision system 108 including one or morecameras capturing digital images of the cans 26 in the zones on theconveyor 20 sends the captured images to the processor 106. From theimages the processor 106 can detect stranded cans and flow problems andalter the normal coil drive sequence to remedy any problems. Forexample, one way that dead spots on a diverter or an in-line conveyorcan be eliminated is by driving the coils with a waveform as shown inFIGS. 15 and 16. The standard ac drive waveform 110 for each phase isamplitude-modulated by a pulse train to produce periodic higher-powerdrive pulses 112. The periodic pulses can occur at fixed or varyingrates. For example, FIGS. 15 and 16 show a 1 kHz drive waveformmodulated by a fixed 8.3 Hz pulse train with a 17% duty cycle and apulse-amplification factor of about 1.2. The capacitance C of the seriescapacitors 105A-C is selected to form a high-Q resonant circuit with thelarge inductance L of the coils 102A-C in each phase. The frequency f ofthe ac drive waveform 110 for each phase is set close to the circuit'snominal resonant frequency f_(r)=1/[2π(LC)^(1/2)]. Because of tolerancesin the actual values of L and C and the fact that the coil driversoperate better driving inductive loads, the frequency f of the ac drivewaveform is set close to, but slightly above, the nominal, ortheoretical, resonant frequency f_(r). The frequency f of the ac drivewaveform is set high enough above the nominal resonant frequency f_(r)to ensure that the reactive impedances X of all the coil circuits arepositive, i.e., inductive, and that the drive frequency f is close tothe circuit's actual resonance frequency—at least as close as theresonant circuit's upper half-power (3 dB) frequency—for any combinationof coils and capacitors. In that way deviations and variations in theinductances and capacitances from their nominal values are accountedfor, and the reactive impedances X do not dominate the resistiveimpedances R, i.e., |X|/R<1.73, or, in other words, the power factor isgreater than 0.5. Coil drivers designed to drive capacitive loads with adrive waveform whose frequency f is slightly below the resonantfrequency f_(r) could alternatively be used in an analogous way toensure that the reactive impedances X of all the coil circuits arenegative, i.e., capacitive, and not dominant, and that the drivefrequency f is close to the circuit's actual resonant frequency. Asanother alternative, one of ordinary skill in the art would be able todesign a conventional closed-loop system to drive the coils at exactlythe resonant frequency f_(r), for which the reactive impedance X wouldbe zero. Any of these resonant coil-driving schemes results in anon-dominant, zero or low reactive impedance and an efficient transferof power to the coils. Exemplary pulse-repetition rates range from about5 Hz to 20 Hz with a duty-cycle range of about 5% to 20%. Exemplarypulse-amplification factors range from about 1.2 to 1.5 or greater. Thehigher-amplitude coil-drive pulses 112 produce periodic increases in themagnetic field and the forces acting on cans slowed or stopped inotherwise low field-strength and force (dead spot) regions to move thecans. The pulsed operation can be run at a fixed pulse frequency andduty cycle, or the processor 106 can direct the controller 100 toproduce drive pulses that clear the dead spot and otherwise enhance canmovement when a stranded or slow-moving can is detected by the visionsystem 108. The advantage of applying short pulses to the ac drivewaveform rather than operating permanently at a fixed, greater amplitudeis that the short pulses free the stranded cans without significantlyincreasing the speed of the unstranded, moving cans, which can result intipping.

Another way of eliminating dead spots is by driving the coils inadjacent zones with phase-shifted waveforms as shown in FIG. 17. Theupper waveform 114 represents the coil drive for one phase in a firstzone; the lower waveform 116 represents the coil drive for thecorresponding phase in an adjacent zone. The phases of the two waveformsdiffer by a phase angle θ, about 90° in this example. And the same phaseshift would exist between the other phases in a multiphase system. Thephase shift between the drive waveforms of adjacent zones clears cansfrom dead spots by creating a component of force that is perpendicularto the main conveying direction as a result of the interaction of theout-of-phase electromagnetic flux waves. The perpendicular component offorce clears the dead spots between the adjacent zones. As in the otherdead-spot-clearing techniques, the phase difference can be fixed oradjusted by the processor 106 when stopped or slow-moving cans aredetected by the vision system 108.

Yet another way that dead spots can be eliminated is by operating coilsin adjacent zones at different frequencies. For example, the coils inone zone could be driven by an 1100 Hz waveform and those in an adjacentzone by an 1102 Hz waveform. Like driving the coils in adjacent zoneswith a phase shift, driving the coils at different frequencies producesa force acting on the cans in a direction perpendicular to the conveyingdirection. The frequency difference can be fixed or can be imposed bythe processor 106 when stranded cans are detected by the vision system108.

All the dead-spot-clearing techniques are usable with electromagneticdiverters or with in-line or diverting electromagnetic conveyors toensure the efficient conveyance of cans from the infeed conveyor to thedischarge conveyor.

Aluminum cans were used throughout the description as exemplaryelectrically conductive conveyed articles. But other electricallyconductive articles containing electrically conductive material, such asaluminum or copper, could be conveyed by the coils described.

What is claimed is:
 1. A conveyor system comprising: a first conveyorconveying electrically conductive articles in a first direction to anexit end; a second conveyor conveying the electrically conductivearticles from an entrance end in a second direction different from thefirst direction; a diverter forming a junction between the exit end ofthe first conveyor and the entrance end of the second conveyor; whereinthe diverter includes: a top surface; an entrance adjacent to the exitend of the first conveyor receiving the electrically conductive articleson the top surface from the exit end of the first conveyor; an exitadjacent to the entrance end of the second conveyor; a plurality ofcoils arranged in a matrix of contiguous first and second zones belowthe top surface, wherein the coils in each of the first zones produce anelectromagnetic flux wave that travels in the first direction and forcesthe electrically conductive articles on the top surface above the zoneto move in the first direction and the coils in each of the second zonesproduce an electromagnetic flux wave that travels in the seconddirection and forces the electrically conductive articles on the topsurface above the zone to move in the second direction, wherein at leastsome of the zones along the entrance are first zones and at least someof the zones along the exit are second zones; wherein some of the coilsin the diverter are in the first zones and the rest of the coils are inthe second zones; wherein the electrically conductive articles aredirected from the entrance to the exit by the coils in the first andsecond zones and onto the second conveyor.
 2. A conveyor system as inclaim 1 wherein the second direction is perpendicular to the firstdirection.
 3. A conveyor system as in claim 1 wherein the coils in eachof the zones are staggered along parallel lines oblique to the first andsecond directions.
 4. A conveyor system as in claim 1 wherein each ofthe first and second zones includes a single coil module having a singleiron core along which all the coils in the zone are wound.
 5. A conveyorsystem as in claim 1 wherein each of the first and second zones includesone or more coil modules, each having the same number of coils.
 6. Aconveyor system as in claim 5 wherein each of the coil modules includesan iron core around which the coils are formed and wherein the iron corein at least some of the coil modules has a stepped structure along atleast one end that mates with the stepped structure on the iron core ofan adjacent coil module in the same zone.
 7. A conveyor system as inclaim 5 wherein the coils in the adjacent coil modules of differentfirst zones or different second zones overlap each other.
 8. A conveyorsystem as in claim 5 wherein the matrix of contiguous first and secondzones is a rectangular matrix of the coil modules.
 9. A conveyor systemas in claim 5 wherein the matrix of contiguous first and second zonesdefines rows of coil modules aligned in the second direction and columnsof coil modules aligned in the first direction.
 10. A conveyor system asin claim 9 wherein the number of coil modules in contiguous first zonesdecreases monotonically row by row away from the entrance.
 11. Aconveyor system as in claim 1 wherein the coils are rectangular with twoshort sides and two long sides and have a magnetic axis parallel to thetop surface and are orthocyclically wound with a crossover region alongone of the sides.
 12. A conveyor system as in claim 11 wherein thecrossover region is along the long side farther from the top surface ofthe diverter.
 13. A conveyor system as in claim 1 comprising amultiphase controller driving the coils in each of the first and secondzones.
 14. A conveyor system comprising: a first conveyor conveyingelectrically conductive articles in a first direction to an exit end; asecond conveyor conveying the electrically conductive articles from anentrance end in a second direction, wherein the angle θ between thefirst direction and the second direction is given by 0°<θ≤90°; adiverter forming a junction between the exit end of the first conveyorand the entrance end of the second conveyor; wherein the diverterincludes: a top surface; an entrance adjacent to the exit end of thefirst conveyor receiving the electrically conductive articles on the topsurface from the exit end of the first conveyor; an exit adjacent to theentrance end of the second conveyor; a plurality of coils arranged inparallel below the top surface and having magnetic axes in a thirddirection oblique to the first direction and producing anelectromagnetic flux wave that forces the electrically conductivearticles on the top surface above the coils to move in the thirddirection, wherein the angle α between the first direction and the thirddirection is given by 0°<α<θ; wherein the electrically conductivearticles are directed from the entrance to the exit by the coils andonto the second conveyor.
 15. A conveyor system as in claim 14 whereinθ=90°.
 16. A conveyor system as in claim 14 comprising a multiphasecontroller driving the coils.
 17. A conveyor system comprising: a firstconveyor conveying electrically conductive articles in a first directionto an exit end; a second conveyor conveying the electrically conductivearticles from an entrance end in a second direction different from thefirst direction; a diverter forming a junction between the exit end ofthe first conveyor and the entrance end of the second conveyor; whereinthe diverter includes: a top surface; an entrance adjacent to the exitend of the first conveyor receiving the electrically conductive articleson the top surface from the exit end of the first conveyor; an exitadjacent to the entrance end of the second conveyor; a plurality ofcoils arranged in an arc below the top surface from the entrance to theexit wherein, in a plan view perpendicular to the top surface, each ofthe coils has a narrow end at the inside of the arc and an oppositewider end at the outside of the arc; wherein the electrically conductivearticles are directed from the entrance to the exit by the coils andonto the second conveyor.
 18. A conveyor system as in claim 17 whereinthe arc subtends an angle of 90°.
 19. A conveyor system as in claim 17wherein the narrow end of the coil is taller than the wider end in adirection perpendicular to the top surface.
 20. A conveyor system as inclaim 17 comprising an iron core around which the coil is formed andwherein the thickness of the iron core is constant along the length ofthe coil.
 21. A conveyor system as in claim 17 comprising iron coresaround which the coils are formed, wherein the thickness of the ironcores increases from the end of the coils at the inside of the arc tothe end of the coils at the outside of the arc.
 22. A conveyor system asin claim 17 comprising iron cores around which the coils are formed,wherein the ratio of the thickness of the coils to the thickness of theiron cores is a constant along the lengths of the iron cores.
 23. Aconveyor system as in claim 17 comprising an iron core around which thecoil is formed, wherein the thickness of the iron core is constant alongits length.
 24. A conveyor system as in claim 17 wherein the coils areorthocyclically wound with the crossover region at the end of the coilcloser to the inside of the arc.
 25. A conveyor system as in claim 17wherein the arc of coils forms an outer arc and the conveyor systemcomprises a second plurality of coils arranged in an inner arc insidethe outer arc.
 26. A conveyor system as in claim 17 comprising amultiphase controller driving the coils.
 27. A conveyor systemcomprising: an electromagnetic conveyor including: a top surface; anentrance over which electrically conductive articles are transferredonto the top surface; an exit over which electrically conductivearticles are transferred off the top surface; a plurality of coilsarranged below the top surface in an array and producing electromagneticflux waves causing forces that move the electrically conductive articlesacross the top surface from the entrance to the exit; a controllerdriving the coils with drive waveforms characterized by a firstamplitude and periodic pulses of a greater second amplitude thatperiodically increase the forces acting on the electrically conductivearticles in low-force regions on the top surface to enhance movement ofthe electrically conductive articles from low-force regions on the topsurface.
 28. A conveyor system as in claim 27 wherein the controllerdrives the coils with the periodic pulses at a fixed rate.
 29. Aconveyor system as in claim 27 wherein the periodic pulses are formed bymodulating the amplitude of the drive waveforms.
 30. A conveyor systemas in claim 27 further comprising a capacitor in series with thecontroller and the coils to form a resonant circuit with the coils witha resonant frequency and wherein the frequency of the drive waveform isclose enough to the resonant frequency to ensure that the reactiveimpedance of the resonant circuit is not dominant.
 31. A conveyor systemas in claim 27 further comprising: a processor; and a vision systemcapturing digital images of the electrically conductive articles beingconveyed on the top surface of the electromagnetic conveyor and sendingthe digital images to the processor; wherein the processor directs thecontroller to drive the coils with the drive waveforms characterized byperiodic pulses whenever stopped or slowed articles are detected in thedigital images.
 32. A conveyor system comprising: an electromagneticconveyor including: a top surface; an entrance over which electricallyconductive articles are transferred onto the top surface; an exit overwhich electrically conductive articles are transferred off the topsurface; a plurality of coils arranged below the top surface inindividual zones and producing electromagnetic flux waves causing forcesthat move the electrically conductive articles through the zones acrossthe top surface from the entrance to the exit; controllers associatedwith the zones and driving the coils with drive waveforms havingdifferent frequencies or phase angles in adjacent zones to enhancemovement of the electrically conductive articles from zone to zone. 33.A conveyor system as in claim 32 wherein the controllers drive the coilswith the drive waveforms having fixed different frequencies or fixedphase angles.
 34. A conveyor system as in claim 32 further comprisingcapacitors in series with the controllers and the coils to form resonantcircuits with the coils with resonant frequencies and wherein thefrequencies of the drive waveforms are close enough to the resonantfrequencies to ensure that the reactive impedances of the resonantcircuits are not dominant.
 35. A conveyor system as in claim 32 furthercomprising: a processor; and a vision system capturing digital images ofthe electrically conductive articles being conveyed on the top surfaceof the electromagnetic conveyor and sending the digital images to theprocessor; wherein the processor directs the controller to drive thecoils with the drive waveforms having different frequencies or phaseangles in adjacent zones whenever stopped or slowed articles aredetected in the digital images.